1. Field of the Invention
The present invention relates to device and method for displaying quality variation measured in the manufacturing process.
2. Description of the Related Art
Methods of establishing associations between quality characteristic values of products and the contents of operation or production conditions have been proposed in order to control the quality of the products.
Japanese Patent Laid-Open No. H09-219347 (laid open on Aug. 19, 1997) discloses a method of obtaining the correlation between device state data representing the state of a manufacturing device and product data such as the yield and electrical characteristics of products on the basis of the time when the products are manufactured.
Japanese Patent Laid-Open No. 2001-293761 (laid open on Oct. 23, 2001) discloses a method of displaying a production achievement ratio, the presence/absence of the occurrence of abnormalities, the presence/absence of change in molding conditions, and quality data in an injection molding device at multiple screens on a common time axis.
Japanese Patent Laid-Open No. 2004-198148 (laid open on Jul. 15, 2004) discloses a method of displaying the record of quality data, the content of change in production conditions, the content of abnormalities in units, and countermeasures thereto on a common time axis.
Japanese Patent Laid-Open No. 2004-186445 (laid open on Jul. 2, 2004) discloses how conditions in a manufacturing process and product inspection data are combined and the correlation between them is analyzed accordingly.
By the conventional methods described above, production conditions and quality data of products are controlled based on the time axis. However, when individual products are sequentially produced using a manufacturing device, these products are not produced at equal time intervals because of time consumed by abnormalities and recovery from them, change in the production speed according to environmental factors and the like. Similarly, prescribed time after the manufacturing time, quality characteristic values of products cannot be measured at equal intervals among these sequentially manufactured products.
Therefore, when variation in a quality characteristic value is displayed based on the time axis, information indicating the number of products measured within a certain time period is lost.
Now assume that for example the manufacturing device has three equivalent manufacturing processing portions, and these portions sequentially output one product at a time. When one of the processing portions suffers from some failure, a quality characteristic value changes in the ratio of one for every three products. More specifically, the quality characteristic value changes in a cycle of three products. In such a case, by the conventional methods, the variation in the quality characteristic value is displayed based on the time axis, and the information indicating the number of products is lost, so that the information about the cycle is also lost. Consequently, the presence of the failure in one of the manufacturing processing portions cannot immediately be identified.
When the manufacturing device and the quality measuring device are different, it takes some time for products to move from the manufacturing device to the quality measuring device, and therefore associations cannot be established between abnormalities in the quality and conditions concerning the manufacturing device simply because their time axes are matched.